This invention relates to a method and apparatus for generating vibration energy useful in a vibrating process such as vibratory screens and in particular to a method and apparatus for generating vibration energy by magnetically orbiting a loosely disposed mass within an apparent rotating magnetic field.
Vibration energy for use in processes has previously been generated by placing one or more imbalanced masses on a shaft and driving the shaft with an external power source. As the shaft on which the imbalanced mass is mounted is rotated, a radially outward centrifugal force coincident with the axis of the shaft and the center of gravity of the imbalanced mass is generated. This design of vibration generator loads the shaft bearings, resulting in wear and a short useful life.
Heretofore, vibration energy has been generated by rotating a shaft having thereon one or more eccentric weights. The centrifugal force thereby generated was transmitted to the device on which the shaft was mounted through the shaft and shaft bearings. As a result the shaft bearings carried the centrifugal load, resulting in rapid bearing wear.
U.S. Pat. No. 2,945,386 addressed this problem. In FIGS. 1-3 an arrangement is disclosed wherein a balanced spool-shaped weight is rotated by an external source. An annular guideway in the spool-shaped weight provides a guideway for passage of a magnetically attractable ball. Permanent magnets are embedded in and rotate with the spool-shaped weight. The magnets are spaced evenly around the axis of the spool-shaped weight and are placed on both sides of the annular passageway so as to attract the magnetic ball therebetween. As the spool-shaped weight is rotated the magnetically attractable rolling element travels in alignment between aligned magnets on the spool-shaped weight thus providing a centrifugal force as the magnetically attractable rolling element rotates about the axis of the spool-shaped weight.
However, such vibration generators require an external mechanical force to propel the rolling weight about the raceway.
Another known vibration generator that eliminates the bearing load problem is disclosed in U.S. Pat. No. 3,135,124 by providing a cylindrical rotor within a cylindrical raceway in which the cylindrical rotor has reaction passages therein such that fluid flowing through the reaction passages produces a reaction that causes the rotor to rotate and to seek a position against the raceway and roll thereon to produce vibration.
In addition, in applications such as screening where vibration energy on both side plates of the screening apparatus was identical, two eccentric weights, one mounted near each side plate of the screening apparatus and further mounted on the same shaft to assure mechanical synchronization, were rotated. Two additional eccentric weights again were mounted near each side plate, on a second shaft. The four eccentric weights were rotated to generate vibration energy. Shaft deflection due to its own weight on long shafts, resulted in shaft failure and limited shaft lengths, and hence the width of a screening apparatus, to approximately ten feet.